Photosensitive variable resistance device



June 28, 1966 A. c. SULESKI PHOTOSENSITIVE VARIABLE RESISTANCE DEVICE 2Sheets-Sheet 1 Filed March 15 1960 FlG.1u.

FIG. 2

FIG. 3

June 28, 1966 A. c. SULESKI 3,258,601

PHOTOSENSITIVE VARIABLE RESISTANCE DEVICE 2 Sheets-Sheet 2 FIG.4

Filed March 15 1960 FIG. 5

FIG. 6

FIG.7

United States Patent 3,258,601 PHOTOSENSITIVE VARIABLE RESISTANCE DEVICEAnthony C. Suleski, Bronx, N.Y., assignor to Hazeltme Research, Inc., acorporation of Illinois Filed Mar. 15, 1960, Ser. No. 15,170 11 Claims.(Cl. 250211) This invention relates to variable resistance devices and,more particularly, to such devices utilizing photosensitive materials.For the purposes of this specification, photosensitive will be definedas meaning sensitive electrically to the action of radiant energy, thesensitivity more particularly referred to being that of conductivity.

In previous variable resistance devices, such as potentiometers, slidingcontacts have generally been required. Inherent in such arrangements isundesirable electrical noise created by the movement of the contacts. Inthe past, it has also been difficult to construct potentiometers withprecision resistance characteristics. For example, complicatedexponential tapers have been especially hard to achieve.

It is an object of this invention to provide a new type of variableresistance device.

It is an additional object of this invention to provide a resistancedevice which avoids one or more disadvantages of prior art arrangements.

It is a further object of this invention to provide a variableresistance device which can be constructed to a high degree ofelectrical accuracy.

' It is a further object of this invention to provide a variableresistance device in which the range over which the resistance can bevaried can be adjusted.

It is a further object of this invention to provide a new type of signalgenerator.

In accordance with the present invention, a variable resistance devicecomprises a first pair of conductors spaced along their length, at leastone additional conductor positioned between the first pair of conductorsso that the spacing between the third conductor and the first pair ofconductors varies over the length of the third conductor. The apparatusfurther comprises a photosensitive layer, whose electrical resistance isdependent upon the illumination of the layer, in contact with each ofthe conductors and extending between them, and means for illuminating avariable portion of the layer, which portion always includes points atwhich the layer contacts each of the conductors, the variable resistancedevice being so constructed and arranged that if a potential is appliedbetween the first pair of conductors, the portion of the potentialexisting between the additional conductor and either one of the firstpair of conductors is determined by the particular portion of the layerwhich is illuminated. For a better understanding of the presentinvention, together with other and further objects thereof, reference ishad to the following description taken in connection with theaccompanying drawings, and its scope will be pointed out in the appendedclaims.

Referring to the drawings:

FIGS. 1a and lb represent one form of Variable resistance device inaccordance with the invention;

FIG. 2 is a development of the surface of the cylinder of FIG. 1;

FIGS. 3 and 4 represent configurations in accordance with the inventioncapable of producing exponential resistance relationships, and

FIGS. 5, 6, and 7 illustrate arrangements suitable for use in signalgenerators for producing sinusoidal wave forms, square wave forms andsine-cosine wave forms, respectively.

Referring now to FIGS. 1 and 2 of the drawings, FIG. 1a shows a variableresistance device in the form of a potentiometer utilizing theinvention, FIG. 1b is an end view of the FIG. la arrangement and FIG. 2is a development of the surface of the cylinder of FIGS. 1a and 1b.

The variable resistance device includes a surface, illustrated as theconcave surface 10 of a hollow ceramic cylinder 11, having thereonconductors shown as the three conductors 12, 13, and 14. Theseconductors may be in the form of gold or silver painted on the cylinderand then fired, or of any other suitable material placed on the surface.The dotted line in FIG. 1a can be considered to represent eitherconductor 12 or conductor 14 of FIG. 2; however, the conductorconfiguration cannot be clearly shown in the FIG. 1a view, and FIG. 2should be referred to for details of conductor layout.

The variable resistance device also includes a photosensitive layer,shown as layer 15, disposed upon said surface and in contact with theconductors. This layer may be composed of any appropriate photosensitiveor photoconductive material, the use and composition of such materialsbeing well known.

The variable resistance device further includes means for illuminating avariable portion of the layer. This means is illustrated as a longfilament source 16 which is surrounded by a hollow opaque cylinder 17having a longitudinal slit 18.

Referring now to FIG. lb, which is an end view of the device of FIG. 1a,it will be seen that the arrangement is such that the illuminationcoming from filament 16 is so constrained by cylinder 17 as to allowonly an area similar to area 19 of FIG. 2 to be illuminated. (Shield 17is shown as a simple split cylinder but it will be appreciated that amore complicated shielding system may be required to accuratelyconstrain the illumination.) By rotating cylinder 17, any desiredportion of the surface 15 can be illuminated.

As shown in FIG. 2, the conductors 12, 13, and 14 may be connected toterminals 20 to allow coupling to external circuitry.

In the operation of the FIG. 1 arrangement, the device may be used as apotentiometer with a resistance between the outer two conductors 12 and14 determined by the characteristics of the photosensitive surface, thephysical dimensions of the device, the quantity and quality ofillumination and the area illuminated. With all these variables heldconstant, the photosensitive layer assumed to be a uniform layer and theilluminated area 19 in the form of a narrow band 19 as shown in FIG. 2,a particular resistance will result between the two outer conductors 12and 14. The middle conductor 13 will have a resistance to each of thetwo outer conductors, the sum of these two resistances equaling theresistance between the conductors 12 and 14 and the ratio of these tworesistances depending upon the particular axial portion (such as theportion illuminated by area 19 in FIG. 2) of the photosensitive layerilluminated. The device can thus be utilized in the manner of anordinary resistive potentiometer, the resistance adjustment beingaccomplished by movement of the illuminated area along thephotosensitive layer.

It will be seen that the resistance range of a device such as describedwill depend on the over-all resistance between conductors 12 and 14.This over-all resistance, in turn, depends upon the quantity and qualityof the illumination striking area 19. Thus, the range of such a devicecan be varied by controlling the characteristics of the illumination. Inthis way a variable resistance device can be constructed using only twoconductors, such as 12 and 14, and arranging for the intensity ofillumination to be varied or by varying the area illuminated (as bychanging the width of area 19) for example.

Referring now to FIGS. 3 and 4, there are shown two surface arrangementswhich may, for example, be utilized in devices similar to that shown inFIG. 1. The conductors of FIG. 3 are arranged so as to give anexponential taper. This taper is achieved by giving conductor 30 theconfiguration of an exponential curve while conductors 31 and 32 have astraight line configuration. Taper as used here is intended to refer tothe relationship between changes in resistance proportions and changesin the area illuminated. Thus, in FIG. 3, if the illumination band 19 ismoved one unit to the left the resistance between conductors 30 and 31will increase by a particular amount. However, if illumination band 19is moved two units to the left the resistance increase betweenconductors will not be twice the particular amount of the one unitmovement, and an exponential equation will be required to describe theactual relationship of resistance change with illumination movement.This device will be said to have an exponential taper.

While the FIG. 3 arrangement may use a straight illumination bandsimilar to 19, it should also be appreciated that a curved orexponential illumination band such as 33 can be used to obtain a moremathematically sophisticated taper. FIG. 4 shows an arrangement similarto that of FIG. 3 except that a plurality of middle conductors 34, 35,36 and 37, each having a different taper, is included in place of thesingle conductor 30 in FIG. 3. In the operation of a device such asthis, connections can be made to one or more of the middle conductorsduring operation.

Referring now to FIGS. 5, 6, and 7, there are shown surface arrangementsof conductors and a photosensitive layer suitable for placement on ahollow cylinder such as that shown in FIG. 1. These surfaces areconstructed so that when placed on a cylinder each conductor forms acontinuous closed curve, and the photosensitive layer forms a closedcylindrical surface. (That is to say, for example, that the ends 50 and51 of conductors 52 connected to each other.) In these arrangements,connections to the conductors can be made by bringing leads through thecylinder and out on the other side, as shown by the leads 53 of FIG.which connect to terminals 54.

In the operation of devices using surfaces such as those shown in FIGS.5, 6, and 7, a potential is applied between the outside conductors (52and 56 in FIG. 5) and an area similar to 19 of FIG. 2 is illuminated,for example, by a long filament and hollow opaque cylinder such as 16and 17 of FIG. 1. The cylinder 17 is then arranged to be continuouslyrotated. In operation, it will be seen that as the cylinder 17 rotatesthe illumination band will travel continuously along the surface and theresult in FIG. 5, which has a sinusoidal middle conductor 55, will be(assuming the potential between conductors 52 and 56 to be a D.-C.potential) a sinusoidal wave form potential ap pearing between terminalsconnecting to conductors 52 and 55. Thus, this device is a sinusoidalwave form signal generator.

FIG. 6 illustrates a surface arrangement which may be utilized in themanner outlined above to produce a square wave output. The operation issimilar to that of the FIG. 5 arrangement except that the changes inpotential appearing between the outside conductor 60 and the middleconductor 61 will be of an abrupt nature and a square wave potentialvariation will result.

The FIG. 7 arrangement may be utilized as a sine-cosine generator. Thus,if a potential is caused to appear between conductors 70 and 71 and thesurface is then illuminated as explained in conjunction with FIG. 5, theresult will be a sine wave form potential variation appearing betweenconductors 71 and 72, and a wave form which has a cosine potentialvariation with respect to the firstmentioned wave form appearing betweenconductors 71 and 73.

While only certain arrangements in accordance with this invention havebeen discussed, it should be appreciated that a large variety of devicesare possible, and the invention is not intended to be limited to theparticular configurations described. For example, while the devicesdiscussed have been primarily concerned with uniform photosensitivelayers, it is obvious that a layer whose thickness, for example, variesin a desired manner, can be utilized with any desired conductorarrangement. Similarly, the quality and quantity of illumination can bevaried or controlled in a desired manner, as can the movement of theillumination beam along the surface and the characteristics of anapplied potential, thereby resulting in a wide variety of possibleresistance variations. It is, therefore, intended in the appended claimsto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. A variable resistance device comprising:

a first pair of conductors spaced along their length;

at least one additional conductor positioned between said first pair ofconductors so that the spacing between said third conductor and saidfirst pair of conductors varies over the length of said third conductor;

a photosensitive layer, whose electrical resistance is dependent uponthe illumination of said layer, in contact with each of said conductorsand extending between them;

and means for illuminating a variable portion of said layer, whichportion always includes points at which said layer contacts each of saidconductors;

the variable resistance device being so constructed and arranged that ifa potential is applied between the first pair of conductors, the portionof said potential existing between said additional conductor and eitherone of said first pair of conductors is determined by the particularportion of the layer which is illuminated.

2. A variable resistance device as described in claim 1, wherein saidfirst pair of conductors are parallel to each other over their length.

3. A variable resistance device as described in claim 1, wherein each ofsaid conductors is metallic and has negligible electrical resistanceover its entire length and effectively all electrical resistance in thecomplete device is provided entirely by the photosensitive layer.

4. A variable resistance device comprising:

a plurality of spaced conductors whose spacing varies as a function oflength, each said conductor having negligible electrical resistance overits entire length;

a photosensitive layer, whose electrical resistance is dependent uponthe illumination of said layer, in contact with each of said conductorsand extending between them;

and means for illuminating a variable portion of said layer, whichportion always includes points at which said layer contacts each of saidconductors;

the variable resistance device being so constructed and arranged thatthe quantity and quality of the illumination are fixed, the size andshape of the illuminated portion of the layer are fixed, eifectively allelectrical resistance in the complete device is provided entirely by thephotosensitive layer and variation in the resistance between theconductors is controlled solely by varying the points along theconductors at which the illuminated portion is positioned.

5. A variable resistance device as described in claim 4, wherein thephotosensitive layer has the form of a hollow cylinder with theconductors in contact with the external surface of the layer andinternal portions of the layer are illuminated.

6. A variable resistance device comprising:

a continuous cylindrical layer of photosensitive material whoseelectrical resistance is dependent upon the illumination of said layer;

a first pair of spaced conductors, each conductor in the form of aclosed continuous loop in contact with said layer over the length of theconductor;

at least one additional conductor spaced between said first pair ofconductors and in contact with said layer over the length of theconductor;

means for illuminating a variable longitudinal portion of said layer,which portion always includes points at which said layer contacts eachof said conductors;

the variable resistance device being so constructed and arranged that ifa potential is applied between the first pair of conductors, the portionof said potential existing between said additional conductor and eitherone of said first pair of conductors is deter mined by the particularportion of the layer which is illuminated.

7. A variable resistance device as described in claim 6, wherein theconductors are in contact with the external surface of the cylindricalphotosensitive layer and internal portions of the layer are illuminated.

8. A variable resistance device as described in claim 6, wherein saidfirst pair of conductors are parallel to each other over their lengthand the spacing of said additional conductor varies as a function of itslength.

9. A variable resistance device, useable for generating a periodictime-varying electrical signal, comprising:

a continuous cylindrical layer of photosensitive material whoseelectrical resistance is dependent upon the illumination of said layer;

a first pair of spaced conductors, each conductor in the form of aclosed continuous loop in contact with said layer over the length of theconductor;

at least one additional conductor spaced between said first pair ofconductors and in contact with said layer over the length of theconductor;

means for illuminating a variable longitudinal portion of said layer,which portion always includes points at which said layer contacts eachof said conductors, and for permitting continuous movement of saidilluminated portion along the length of said conductors;

the variable resistance device being so constructed and arranged that ifa potential is applied between the first pair of conductors, the portionof said potential existing between said additional conductor and eitherone of said first pair of conductors is determined by the particularportion of the layer which is illuminated and a periodic time-varyingelectrical signal is generated by causing the illuminated portion toperiodically move along the entire length of said conductor.

10. A variable resistance device as described in claim 9, wherein:

the first pair of conductors are parallel to each other over theirlength, the additional conductor is a closed continuous loop and thespacing between said additional conductor and said first pair ofconductors varies as a sine function;

the construction being such that a time-varying sinewave electricalsignal can be generated.

11. A variable resistance device as described in claim 9, wherein:

the first pair of conductors are parallel to each other over theirlength, the additional conductors are a series of short segments withdifferent spacings from the parallel conductors and all of said segmentsare electrically interconnected by external wiring not in contact withthe photosensitive layer;

the construction being such that a time-varying squarewave electricalsignal can be generated.

References Cited by the Examiner RALPH G. NILSON, Primary Examiner.RICHARD M. WOOD, Examiner. W. STOLWEIN, Assistant Examiner.

1. A VARIABLE RESISTANCE DEVICE COMPRISING: A FIRST PAIR OF CONDUCTORSSPACED ALONG THEIR LENGTH; AT LEAST ONE ADDITIONAL CONDUCTOR POSITIONEDBETWEEN SAID FIRST PAIR OF CONDUCTORS SO THAT THE SPACING BETWEEN SAIDTHIRD CONDUCTOR AND SAID FIRST PAIR OF CONDUCTORS VARIES OVER THE LENGTHOF SAID THIRD CONDUCTOR; A PHOTOSENSITIVE LAYER, WHOSE ELECTRICALRESISTANCE IS DEPENDENT UPON THE ILLUMINATION OF SAID LAYER, IN CONTACTWITH EACH OF SAID CONDUCTORS AND EXTENDING BETWEEN THEM; AND MEANS FORILLUMINATING A VARIABLE PORTION OF SAID LAYER, WHICH PORTION ALWAYSINCLUDES POINTS AT WHICH SAID LAYER CONTACTS EACH OF SAID CONDUCTORS;